Production Of High-Pressure Gaseous Nitrogen

ABSTRACT

The present invention is an improved process for producing elevated pressure nitrogen. This method includes providing an air separation unit with at least two columns, an LP column and an MP column, and cooling a compressed feed air stream in a heat exchanger, then expanding the resulting cooled feed air stream in an expander, thereby producing a quantity of work and a cooled inlet air stream, feeding the cooled inlet air stream into the LP column. Then extracting a nitrogen stream from the MP column, and warming a first portion of the nitrogen stream in the heat exchanger, thereby producing a product nitrogen stream. Then compressing a second portion of the nitrogen stream in a compressor, thereby producing medium pressure nitrogen stream, and introducing the medium pressure nitrogen stream into an LP column vaporizer. Then extracting a second nitrogen stream from the LP column, and cooling the second nitrogen stream in a condenser thereby producing a liquid nitrogen stream. Then introducing a first portion of the liquid nitrogen stream into the LP column, increasing the pressure of a second portion of the liquid nitrogen stream, thereby producing a pressurized liquid nitrogen stream, and introducing a first portion of the pressurized liquid nitrogen stream into the MP column, and export a second portion of the pressurized liquid nitrogen stream as product.

FIELD OF INVENTION

The present invention relates to a process and an installation for producing nitrogen under pressure.

BACKGROUND

In installations for producing nitrogen under pressure, the nitrogen is usually produced directly at the pressure of use, for example between 5 and 10 bars. Purified air, compressed slightly above this pressure, is distilled so as to produce the nitrogen at the top of the column and the reflux is achieved by expansion of the “rich liquid” (liquid at the base of the column formed by air enriched with oxygen) and cooling of the condenser at the top of the column by means of this expanded liquid. The rich liquid is thus vaporized at a pressure of between about 3 and 6 bars.

If the size of the installation justifies this, the vaporized rich liquid is passed through an expansion turbine so as to maintain the installation in the cold state but, often, this refrigerating production is excessive, which corresponds to a loss of energy. In the opposite hypothesis, the cold state is maintained by an addition of liquid nitrogen coming from an exterior source, and the vaporized rich liquid is simply expanded in a valve and then travels through the thermal exchange line serving to cool the initial air. Consequently, here again, a part of the energy of the vaporized rich liquid is lost.

SUMMARY

The present invention is an improved process for producing elevated pressure nitrogen. This method includes providing an air separation unit with at least two columns, an LP column (101) and an MP column (102), and cooling a compressed feed air stream (104) into a heat exchanger (106), then expanding the resulting cooled feed air stream (107) in an expander (139), thereby producing a quantity of work and a cooled inlet air stream (140), feeding said cooled inlet air stream into said LP column. Then extracting a nitrogen stream (133) from said MP column, and warming a first portion (119) of said nitrogen stream in said heat exchanger, thereby producing a product nitrogen stream (135). Then compressing a second portion (120) of said nitrogen stream in a compressor (123), thereby producing medium pressure nitrogen stream (124), and introducing said medium pressure nitrogen stream into an LP column vaporizer 138. Then extracting a second nitrogen stream (125) from said LP column, and cooling said second nitrogen stream in a condenser (113) thereby producing a liquid nitrogen stream (126). Then introducing a first portion (127) of said liquid nitrogen stream into said LP column, increasing the pressure of a second portion (128) of said liquid nitrogen stream, thereby producing a pressurized liquid nitrogen stream (129), and introducing a first portion (130) of said pressurized liquid nitrogen stream into said MP column, and export a second portion (131) of said pressurized liquid nitrogen stream as product.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a portion of one embodiment of the present invention.

FIG. 2 is a schematic representation of the remaining portion of one embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Turning now to FIG. 1 and FIG. 2, which complementarily illustrate one embodiment of the present invention. In the interest of clarity, element numbers are consistent between these two figures. Compressed, filtered, and pre-cooled air stream 103 may be split into first air stream portion 105 and second air stream portion 104. First air stream portion 105 enters first auxiliary heat exchanger 108 where it is cooled by indirect heat exchange with at least stream 114, thus producing cooled first portion 109, which is combined with stream 107. Second air stream portion 104 enters main heat exchanger 106 where it is cooled by indirect heat exchange with at least stream 119, thus producing cooled second portion 107. The combined stream 107, 109 is introduced into expander 139, thereby producing expanded stream 140, which is then introduced into LP column 101.

Rich liquid stream 110 is removed from the bottom of MP distillation column 102, passed through second auxiliary heat exchanger 111 where it is cooled by indirect heat exchange with at least stream 116, thereby producing cooled rich liquid stream 112 which is then introduced into LP distillation column 101. Vapor stream 116 exits the top of condenser 113, and liquid stream 114 exits the bottom of condenser 113. After being in indirect heat exchange with first air stream portion 105, liquid stream 114 is warmed, thereby producing warm stream 115. After being in indirect heat exchange with rich liquid stream 110, vapor stream 116 is warmed, thereby producing warmed stream 117.

First nitrogen stream 133 is extracted from MP column 102 and split into at least into first nitrogen portion 119, and second nitrogen portion 120. First nitrogen portion 119 is warmed in main heat exchanger 106, thereby producing product nitrogen stream 135. Optionally, product nitrogen stream 135 may be further compressed in product compressor 136, thereby producing pressurized product nitrogen stream 137. Second nitrogen portion 120 is compressed in compressor 123 thereby producing medium pressure nitrogen stream 124, which is introduced into LP distillation column vaporizer 138.

Second nitrogen stream 125 is extracted from LP distillation column 101, and cooled in condenser 113, thereby producing liquid nitrogen stream 126. Liquid nitrogen stream 126 is split into at least first liquid nitrogen portion 127 and second liquid nitrogen portion 128. First liquid nitrogen portion 127 is introduced into LP distillation column 101. The pressure of second liquid nitrogen portion 128 is increased thereby producing pressurized liquid nitrogen stream 129. Pressurized liquid nitrogen stream is split into at least first pressurized nitrogen portion 130 and second pressurized nitrogen portion 131. First pressurized nitrogen portion 130 is introduced into MP distillation column 102. Second pressurized nitrogen portion 131 is exported as product.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. 

1. An improved process for producing elevated pressure nitrogen, comprising; providing an air separation unit with at least two columns, a LP column (101) and an MP column (102), cooling a compressed feed air stream (103) in a heat exchanger (106), then expanding the resulting cooled feed air stream (107) in an expander (139), thereby producing a quantity of work and a cooled inlet air stream (140), feeding said cooled inlet air stream into said LP column, extracting a nitrogen stream (133) from said MP column, warming a first portion (119) of said nitrogen stream in said heat exchanger, thereby producing a product nitrogen stream (135), compressing a second portion (120) of said nitrogen stream in a compressor (123), thereby producing medium pressure nitrogen stream (124), introducing said medium pressure nitrogen stream into an LP column vaporizer, extracting a second nitrogen stream (125) from said LP column, cooling said second nitrogen stream in a condenser (113) thereby producing a liquid nitrogen stream (126), introducing a first portion (127) of said liquid nitrogen stream into said LP column, increasing the pressure of a second portion (128) of said liquid nitrogen stream, thereby producing a pressurized liquid nitrogen stream (129), and introducing a first portion (130) of said pressurized liquid nitrogen stream into said MP column, and export a second portion (131) of said pressurized liquid nitrogen stream as product.
 2. The process of claim 1, wherein said product nitrogen stream is further compressed in a product compressor (136), thereby producing a pressurized product nitrogen stream (137).
 3. The process of claim 1, further comprising; removing a vapor stream (116) from said condenser (113), removing a rich liquid stream (110) from said MP column (102). providing a second auxiliary heat exchanger (111), Introducing said vapor stream and said rich liquid stream into said second auxiliary heat exchanger, thereby producing a cold rich liquid stream (112) and a warmed stream (117). 